Department of Applied Mathematics, The Hong Kong Polytechnic University, Hong Kong, China.
Int J Environ Res Public Health. 2022 Feb 17;19(4):2282. doi: 10.3390/ijerph19042282.
(1) Background: The coronavirus 2019 (COVID-19) pandemic has caused multiple waves of cases and deaths in the United States (US). The wild strain, the Alpha variant (B.1.1.7) and the Delta variant (B.1.617.2) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were the principal culprits behind these waves. To mitigate the pandemic, the vaccination campaign was started in January 2021. While the vaccine efficacy is less than 1, breakthrough infections were reported. This work aims to examine the effects of the vaccination across 50 US states and the District of Columbia. (2) Methods: Based on the classic Susceptible-Exposed-Infectious-Recovered (SEIR) model, we add a delay class between infectious and death, a death class and a vaccinated class. We compare two special cases of our new model to simulate the effects of the vaccination. The first case expounds the vaccinated individuals with full protection or not, compared to the second case where all vaccinated individuals have the same level of protection. (3) Results: Through fitting the two approaches to reported COVID-19 deaths in all 50 US states and the District of Columbia, we found that these two approaches are equivalent. We calculate that the death toll could be 1.67-3.33 fold in most states if the vaccine was not available. The median and mean infection fatality ratio are estimated to be approximately 0.6 and 0.7%. (4) Conclusions: The two approaches we compared were equivalent in evaluating the effectiveness of the vaccination campaign in the US. In addition, the effect of the vaccination campaign was significant, with a large number of deaths averted.
（1）背景：2019 年冠状病毒病（COVID-19）大流行在美国（美国）造成多波病例和死亡。野生株、阿尔法变异株（B.1.1.7）和德尔塔变异株（B.1.617.2）是这些波的主要罪魁祸首。为了减轻大流行，疫苗接种运动于 2021 年 1 月开始。尽管疫苗效力低于 1，但已报告突破性感染。这项工作旨在研究 50 个美国州和哥伦比亚特区的疫苗接种效果。（2）方法：基于经典的易感-暴露-感染-恢复（SEIR）模型，我们在感染和死亡之间添加了一个延迟类，一个死亡类和一个接种疫苗类。我们比较了我们新模型的两个特殊情况来模拟疫苗接种的效果。第一种情况阐述了接种疫苗的个人是否有完全的保护，而第二种情况是所有接种疫苗的个人都有相同水平的保护。（3）结果：通过将这两种方法应用于报告的美国所有 50 个州和哥伦比亚特区的 COVID-19 死亡病例，我们发现这两种方法是等效的。我们计算，如果没有疫苗，大多数州的死亡人数可能会增加 1.67-3.33 倍。估计中位和平均感染病死率约为 0.6%和 0.7%。（4）结论：我们比较的两种方法在评估美国疫苗接种运动的效果方面是等效的。此外，疫苗接种运动的效果显著，避免了大量死亡。
